Conducting mechanism in the epitaxialp-type transparent conducting oxideCr2O3:Mg

Abstract

Epitaxial p-type transparent conducting oxide (TCO) Cr 2 O 3 :Mg was grown by electron-beam evaporation in a molecular beam epitaxy system on c-plane sapphire. The influence of Mg dopants and the oxygen partial pressure were investigated by thermoelectric and electrical measurements. The conduction mechanism is analyzed using the small-polaron hopping model, and hopping activation energies have been determined, which vary with doping concentration in the range of 210-300 ± 5 meV. Films with better conductivity were obtained by postannealing. The effect of postannealing is discussed in terms of a crystallographic reordering of the Mg dopant. The highest Seebeck mobilities obtained from thermoelectric measurements are of the order of 10 −4 cm 2 V −1 s −1 . We investigate the fundamental properties of a Mg dopant in a high crystalline quality epitaxial film of a binary oxide, helping us understand the role of short range crystallographic order in a p-type TCO in detail.

Low Valence Cation Doping of Bulk Cr2O3: Charge Compensation and Oxygen Vacancy Formation

“…[30][31][32][33] Doping of Cr 2 O 3 with Mg has been documented to change the electronic structure to induce p-type semiconductor behavior by creating a hole that arises from replacing a Cr 3+ cation with an Mg 2+ dopant [34][35][36][37][38][39] however, the optical properties eventually degrade over time, thus making the material inactive. To improve the optical and electronic properties of Cr 2 O 3 and overcome the issues associated with Mg: Cr 2 O 3 , co-doping with Mg and N was examined.…”

“…To improve the optical and electronic properties of Cr 2 O 3 and overcome the issues associated with Mg: Cr 2 O 3 , co-doping with Mg and N was examined. 36,40,41 Nitrogen doping was found to improve the transmission properties and electronic 4 conductivity of Cr 2 O 3 through band gap widening and the presence of NO 3 -in the system; Mg doped Cr cation site is uncompensated, and displays p-type conductivity under optimal growth conditions. 42 No conductivity is found under O-poor conditions, where Mg is likely to be compensated.…”

Spray pyrolysis growth of a high figure of merit, nano-crystalline, p-type transparent conducting material at low temperature

“…The polaronic nature of CuCrO 2 has already been reported extensively 33 and motivated by this we use the SPH model to estimate a mobility value. Within this model the Seebeck coefficient can be used as a direct mea- sure of the fraction of occupied carrier sites 7,9 , c. This is related to the carrier concentration p by p=Nc, where the density of conducting sites N can be calculated using the unit cell volume of the CuCrO 2 crystal and the number of Cu atoms per unit cell (2.5×10 22 cm −3 ). From this p it is possible to estimate a mobility of 6.4×10 −3 cm 2 /Vs for a sample with a conductivity of 12 S/cm (the highest conductivity at room temperature for our films).…”

“…5 Since then the field has extended to other materials such as oxychalcogenides, spinels and α-Cr 2 O 3 . [6][7][8][9] One of the delafossites, CuCrO 2 , has shown promise as a p-type TCM due to reports of high conductivity when doped with Mg. 10 However this is typically only achieved by physical vapour deposition (PVD) which is a relatively slow and costly technique in comparison to other depostion methods. CuCrO 2 has also been grown by chemical vapour deposition (CVD) using the metal-organic Acetylacetonate (acac) precursors Cr(acac) 3 and Cu(acac) 2 at 550 • C, resulting in polycrystalline films with conductivity of 0.86 S/cm (figure of merit (FOM) ≈ 45 µS).…”

“…The T and R values are the average The absorption spectra of Cu deficient CuCrO2 is compared to α-Cr2O3:Mg. 9 All measurements were taken with air as a reference.…”